In a photon-conductive fiber bundle which is bifurcated at one end of its length and combined at the other end, when a light beam enters into the fiber bundle from one of the bifurcated side ends, the light beam passes through the bundle and emerges out of the combined end. The light beam then is reflected on an outside reflector face to turn back into the fiber bundle and emerge out from the other bisected end.
The photon-conductive fiber bundle having such construction is generally used as a light pen serving as an input detector end for photo-optimetric sensor or other similar apparatus. The light pen used for such purposes conventionally is contacted at its end with the reflection label surface upon every scanning so that the end of such light pen suffers wear and deformation due to mechanical friction or rubbing. Such wear is further accelerated, particularly on the tip portion, if the pen is treated roughly or used by different persons because the contact pressure (of the pen against the label surface) is varied according to the individual person's touch who use it. Particularly, in a light pen which is small in diameter at the combined end of the fiber bundle and has high resolving power, deformation of the scanning face of the light pen is increased proportionally to wear of the tip portion, causing change in the light entering and emerging conditions, making it unable to obtain correct results in scanning.
In the past, if such is occasioned, there has been no alternative but to replace the entire light pen with a new one even in the case where the tip portion alone has suffered excessive wear.
Examples of prior art light pens are to be found in U.S. Pat. Nos. 3,758,782; 3,749,932; and 3,509,353.